1. Field of the Invention
This invention relates to liquid crystal light valve (LCLV) projectors. More specifically, this invention relates to optical arrangements used in full color LCLV image projectors.
While the present invention is described herein with reference to an illustrative embodiment for a particular application, it is understood that the invention is not limited thereto. Those having ordinary skill in the art and access to the teachings provided herein will recognize additional modifications, applications and embodiments within the scope of the present invention.
2. Description of the Related Art
The development of the liquid crystal light valve has facilitated substantial progress in the state of the art of high quality large screen projection systems. The reflective mode liquid crystal light valve is a thin film multilayer structure comprising a liquid crystal layer, a dielectric mirror, a light blocking layer, and a photoresponsive layer sandwiched between two transparent electrodes. A polarized projection beam is directed through the liquid crystal layer to the dielectric mirror. An input image of low intensity light, such as that generated by a cathode ray tube is then applied to the photoresponsive layer thereby switching the electric field across the electrodes from the photoresponsive layer onto the liquid crystal layer to activate the liquid crystal. The beam of linearly polarized projection light reflected from the dielectric mirrors is polarization modulated in accordance with the input image incident on the photoconductor from a source of writing light such as a cathode ray tube (CRT). Therefore, the light valve will convert a high intensity beam of polarized light into a polarization modulated replica of a high resolution input image. (U.S. Pat. No. 4,019,807 issued to D. D. Boswell on Apr. 26, 1977 disclosed such a high performance reflective mode liquid crystal light valve.) The resultant beam of high intensity polarization modulated light can be projected with magnification to produce a high brightness image on a viewing screen.
The first large screen projection systems based on liquid crystal light valve technology produced a projection image which was essentially monochromatic. A single light valve was used to modulate the polarization state of a monochromatic beam. Such a system is described in an article entitled "Application of the Liquid Crystal Light Valve to a Large Screen Graphics Display" published in the 1979 Society for Information Display (SID), International Symposium, Digest of Technical Papers, May 1979, pp. 22-33. The display system described in this paper projects a large scale image having yellow-white characters on a dark blue background.
Subsequent advances in the art have led to the development of full color large screen projection systems using multiple liquid crystal light valves. (See U.S. Pat. No. 4,425,028 issued to R. J. Gagnon and R. T. Carson on Jan. 10, 1984.) These full color projection systems typically direct three beams of polarized light to three separate liquid crystal light valves. Each light valve is controlled by the input image received from a separate CRT. Thus, the light valves provide three high intensity polarization modulated beams which are recombined for projection.
These conventional full color liquid crystal light valve image projection systems direct separate red, green and blue beams of polarized light in at least two directions. As the liquid crystal surface of a light valve must be oriented at a ninety degree angle with respect to the incident light beam, this necessitates the use of physically separate, individual light valves oriented in at least two different directions. As liquid crystal light valves are somewhat costly, the use of multiple light valves adds significantly to the cost of the LCLV projection system.
Accordingly, there is a need in the art for a compact optical arrangement for full color liquid crystal light valve image projection which would not require multiple liquid crystal light valves.